Solid free-form fabrication methods for the production of dental restorations

ABSTRACT

Solid free form fabrication techniques such as fused deposition modeling and three-dimensional printing are used to create a dental restoration. Three-dimensional printing includes ink-jet printing a binder into selected areas of sequentially deposited layers of powder. Each layer is created by spreading a thin layer of powder over the surface of a powder bed. Instructions for each layer may be derived directly from a CAD representation of the restoration. The area to be printed is obtained by computing the area of intersection between the desired plane and the CAD representation of the object. All the layers required for an aesthetically sound restoration can be deposited concurrently slice after slice and sintered/cured simultaneously. The amount of green body oversize is equivalent to the amount of shrinkage which occurs during sintering or curing. While the layers become hardened or at least partially hardened as each of the layers is laid down, once the desired final shaped configuration is achieved and the layering process is complete, in some applications it may be desirable that the form and its contents be heated or cured at a suitably selected temperature to further promote binding of the powder particles.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10/874,077 filed Jun. 22, 2004, now abandoned which is acontinuation-in-part application of U.S. application Ser. No.10/053,430, filed Oct. 22, 2001, now U.S. Pat. No. 6,808,659 which is acontinuation-in-part application of U.S. application Ser. No. 09/946,413filed Sep. 5, 2001, now U.S. Pat. No. 6,821,462, which is acontinuation-in-part of U.S. application Ser. No. 09/350,604 filed Jul.9, 1999, now U.S. Pat. No. 6,322,728, which claims priority to U.S.Provisional Application Ser. No. 60/092,432 filed on Jul. 10, 1998, andwhich U.S. application Ser. No. 10/874,077 is a continuation-in-partapplication of U.S. application Ser. No. 10/027,017 filed Dec. 18, 2001,now U.S. Pat. No. 7,011,522, which is a divisional of U.S. applicationSer. No. 09/376,921, filed Aug. 18, 1999, now U.S. Pat. No. 6,354,836,which claims priority to U.S. Provisional Application No. 60/097,216,filed Aug. 20, 1998, and which U.S. application Ser. No. 10/874,077 is acontinuation-in-part application of U.S. application Ser. No.10/857,482, filed May 28, 2004, now U.S. Pat. No. 7,655,586 which claimspriority to U.S. Provisional Application No. 60/474,166, filed May 29,2003, all of which are hereby incorporated by reference.

FIELD OF THE INVENTION

This invention relates to dental restorations made from ceramics,glass-ceramics, metals, alloys, and polymeric composite materials usingsolid free-form fabrication methods.

BACKGROUND OF THE INVENTION

The fabrication of current all-ceramic dental restorations oftenrequires extensive labor and time and the proficiency of highly skilledtechnicians. Many state-of-the-art dental restorations reveal a sense ofartistry that can typically only be achieved manually or “by hand.”While aesthetics are preserved with this process, microstructuralinhomogeneities may appear, affecting strength and reliability. Theindustry has attempted to automate this process by, for example,pressing crowns. Although pressable crowns reduce some of the skill timerequired, about two hours of concerted effort is necessary to complete acrown. Pressed crowns may also suffer from similar strength andreliability problems typical of “hand made” crowns.

Computer assisted design/computer assisted milling (CAD/CAM) processesand equipment have been recently introduced into the dental industry. Inthese processes, a three-dimensional image of a tooth to be restored iscreated along with the teeth surrounding the tooth in an effort tocreate a dental restoration which is to be placed over the tooth. Thisimage is displayed on a computer screen. Based on the tooth andsurrounding teeth, the dental technician may then select a tooth from aplurality of tooth forms stored in the computer to best fit the tooth tobe restored. The selected tooth is projected onto the tooth to berestored until an optimum positioning and fit of the dental restorationis achieved. The digital data concerning the dental restoration thusformed are supplied to a numerically controlled milling machineoperating in three dimensions. The milling machine cuts a blank of metalor porcelain material into the dental restoration design based on thedata supplied.

Commercially available systems such as CEREC™ from Siemens, PROCERA®from Nobel Biocare AG, and CICERO® from Cicero Dental Systems, haveattempted to reduce labor and increase structural reliability. However,the necessary machining steps limit the choice of materials that can beused in dental restorations and sometimes compromise the strength and/oraesthetics of the finished restoration.

One of the current limitations of the CAD/CAM approach, which is noteasy to overcome, is the fact that currently available systems at bestproduce copings that require veneering layers to provide a naturalappearance. Consequently, final processing of the crown is still in thehands of dental technicians which may limit the resulting structuralreliability of the restoration. The existing commercial CAD/CAM systemsare unable to produce full crowns. Some of the systems can machineinlays/onlays from a solid ceramic block and are not able to producecrowns or even copings. Others produce copings that make a core of thecrown that can fit on the prepared tooth but require additional work bydental technicians to provide final shapes and esthetics. This entailsmanual building and firing of porcelain layers on top of a copingreceived from the CAD/CAM facility. Supposedly, one or more systems willbe able to automate forming of successive veneering layers of porcelainon top of a CAD/CAM coping which will involve sintering of consecutiveporcelain layers following their forming by machining or pressing. Thisis an automation of steps that are otherwise performed by dentaltechnicians and very well may not be practically advantageous.

One of the key limitations intrinsic to CAM methods is the fact thatmachining is not competitive technology for mass production of parts andcomponents of any kind including dental restorations, e.g. dentures andcrowns. At any given period of time one cutting tool can be used tomachine only one part and can not be concurrently used to machineanother part.

It is desirable that the automation of the manufacture of dentalrestorations be conducive to mass production of restorations. It isbeneficial that the automation of the manufacture of dental restorationsbe efficient and useful for a variety of materials.

SUMMARY OF THE INVENTION

These and other objects and advantages are accomplished by the processherein directed to solid free-form (SFF) fabrication of dentalrestorations. SFF techniques can be used directly to manufacture singleand multi-unit frameworks, cores, net shape and near-net shape dentalarticles or alternatively SFF methods can be utilized indirectly tomanufacture substrates, dies, models, near-net shapes, shells, andwax-ups that will be used in manufacturing dental restorations. Amongdirect solid free-form fabrication techniques, three dimensionalprinting and fused deposition modeling are preferred because bothceramic and resin-based composite dental restorations can be produced insolid (e.g. denture teeth) or multilayered form (e.g. crowns).Three-dimensional printing is the most preferred direct method formass-production of dental restorations. Digital light processing (DLP)is the most preferred indirect method for production of substrates thatcan be converted to dental articles by various coating or depositiontechniques such as gel casting, slip casting, slurry casting, pressureinfiltration, dipping, colloidal spray deposition or electrophoreticdeposition.

Three-dimensional printing is used to create a dental restoration byink-jet printing a binder into selected areas of sequentially depositedlayers of powder. Each layer is created by spreading a thin layer ofpowder over the surface of a powder bed. Instructions for each layer maybe derived directly from a CAD representation of the restoration. Thearea to be printed is obtained by computing the area of intersectionbetween the desired plane and the CAD representation of the object. Allthe layers required for an aesthetically sound restoration can bedeposited concurrently slice after slice and sintered/curedsimultaneously. The amount of green body oversize is equivalent to theamount of shrinkage which occurs during sintering or curing. While thelayers become hardened or at least partially hardened as each of thelayers is laid down, once the desired final shaped configuration isachieved and the layering process is complete, in some applications itmay be desirable that the form and its contents be heated or cured at asuitably selected temperature to further promote binding of the powderparticles. The individual sliced segments or layers are joined by one ormore binders to form the three dimensional structure. The unbound powdersupports temporarily unconnected portions of the component as thestructure is built but is removed after completion of printing.

BRIEF DESCRIPTION OF THE DRAWINGS

Features of the present invention are disclosed in the accompanyingdrawings, wherein similar reference characters denote similar elementsthroughout the several views, and wherein:

FIG. 1 is a cross-sectional view of a shell formed by rapid prototyping;

FIG. 2 is an elevational view of a model that has been formed from theshell of FIG. 1;

FIG. 3 is a cross-sectional view of a shell 10 with die 20 formedtherein;

FIG. 4 is an elevational view of a plug for use in the shell of FIG. 3;

FIG. 5 is a cross-sectional view of a shell for use in the lost waxprocess;

FIG. 6 is a cross-sectional view of a space made from the shell in FIG.5;

FIG. 7 is a perspective view of working dies used in the process herein;

FIG. 8 is an elevational view of a series of copings attached to abuilding platform;

FIG. 9 is an elevational view of a series of copings attached to abuilding platform ready for insertion into a suspension of chargedparticles; and

FIG. 10 is an elevational view of a series of copings attached to abuilding platform ready for insertion into a slip bath.

DESCRIPTION OF THE INVENTION

A number of techniques have been developed in recent years that areknown under the generic name of solid free-form (SFF) fabrication oralso known as rapid prototyping and are successfully used for net-shapemanufacturing of advanced materials (ceramics, polymers) into small andcomplex shapes. These techniques are similar to CAD/CAM techniques inthat the digital representation of the final shape and itsimplementation is designed and controlled by a computer. However, themachining step in these techniques is substituted by other computerassisted net-shaping techniques including but not limited tothree-dimensional printing, selective area laser deposition or selectivelaser sintering (SLS), electrophoretic deposition, robocasting, fuseddeposition modeling (FMD), laminated object manufacturing (LOM),stereolithography, photostereolithography and digital light processing(DLP). Most of these techniques were developed for net-shapedfabrication of polymeric or wax parts, however, some of them, such asthree-dimensional printing and fused deposition modeling can be used tobuild complex shapes from ceramic or even metallic materials as well. Alarge variety of ceramic, polymeric and composite materials can befabricated into complex shapes using these techniques. U.S. Pat. Nos.5,340,656, 5,490,882, 5,204,055, 5,518,680, 5,490,962, 5,387,380,5,700,289, and 4,672,032 are directed to solid free-form fabricationmethods and techniques and are hereby incorporated by reference.

In this invention, SFF techniques are used to make dental restorationsand various dental articles including but not limited to denture teeth,crowns, bridges, space maintainers, tooth replacement appliances,orthodontic parts, orthodontic retainers, dentures, posts, jackets,inlays, onlays, facings, veneers, facets, implants, abutments, splints,partial crowns, teeth, cylinders, pins, and connectors. SFF techniquescan be used directly to manufacture single and multi-unit frameworks,cores, net shape or near-net shape dental articles or alternatively SFFmethods can be utilized indirectly to manufacture substrates, dies,models, near-net shapes, shells, and wax-ups that will be used inmanufacturing dental articles or restorations. Among direct solidfree-form fabrication techniques, three-dimensional printing and fuseddeposition modeling are preferred because both ceramic and resin-basedcomposite dental articles or restorations can be produced in solid (e.g.denture teeth) or multilayered form (e.g. crowns). Three-dimensionalprinting is the most preferred direct method for mass-production ofdental restorations. DLP is the most preferred indirect method forproduction of substrates that can be converted to dental articles byvarious coating or deposition techniques such as gel casting, slipcasting, slurry casting, pressure infiltration, dipping, colloidal spraydeposition or electrophoretic deposition.

Similarly to CAD/CAM methods, the design of the restoration is carriedby a CAD device which uses at least two inputs: (1) the digital imagetaken optically directly from a mouth of the patient (opticalimpression) or created by digitizing the impression/die by contact or byan optical digitizer; and (2) a library of teeth shapes and forms. CADdevices assure both natural-like shape and proper function of therestoration. Both optical and contact digitizers providing input (1)above are described in the literature and some of them are commerciallyavailable. The specific techniques may require additional software tobuild the shape according to the CAD file.

In one of the embodiments of the present invention, a three-dimensionalprinting machine is used for mass-production of dental restorationsincluding, but not limited to denture teeth, bridges, crowns, bridges,space maintainers, tooth replacement appliances, orthodontic retainers,dentures, posts, jackets, inlays, onlays, facings, veneers, facets,implants, abutments, splints, partial crowns, teeth, cylinders, pins,and connectors. Suitable printing devices include both those with acontinuous jet stream print head and a drop-on-demand stream print head.A high speed printer of the continuous type may be used which has a lineprinting bar containing approximately 1500 jets which can deliver up to60 million droplets per second in a continuous fashion and can print atspeeds up to 900 feet per minute. Both raster and vector apparatuses canbe used. A raster apparatus is where the printhead goes back and forthacross the bed with the jet turning on and off. This can have problemswhen the material is likely to clog the jet upon settling. A vectorapparatus is similar to an x-y printer. Although potentially slower, thevector printer may yield a more uniform finish.

Three-dimensional printing is used to create a dental restoration byink-jet printing a binder into selected areas of sequentially depositedlayers of powder. Each layer is created by spreading a thin layer ofpowder over the surface of a powder bed. The powder bed is supported bya piston which descends upon powder spreading and printing of eachlayer, or conversely, the ink jets and spreader are raised afterprinting of each layer and the bed remains stationary. Instructions foreach layer may be derived directly from a CAD representation of therestoration. The area to be printed is obtained by computing the area ofintersection between the desired plane and the CAD representation of theobject. The individual sliced segments or layers are joined to form thethree dimensional structure. The unbound powder supports temporarilyunconnected portions of the component as the structure is built but isremoved after completion of printing.

The three-dimensional printing apparatus includes a powder dispersionhead which is driven reciprocally in a shuttle motion along the lengthof the powder bed. A linear stepping motor assembly is used to move thepowder distribution head and the binder deposition head. The powdermaterial is dispensed in a confined region as the dispensing head ismoved in discrete steps along the mold length to form a relatively looselayer having a typical thickness of about 100 to about 200 microns. Allthe layers required for an aesthetically sound restoration can bedeposited concurrently slice after slice and sintered/curedsimultaneously. The amount of green body oversize is equivalent to theamount of shrinkage which occurs during sintering or curing. Althoughpowder is used herein to identify the material, the material may includeparticles of any shape including fibers, rod-shaped particles, sphericalparticles, or any shape or form of material used in the manufacture ofdental restorations. An ink jet print head having a plurality of ink-jetdispensers is also driven by the stepping motor assembly in the samereciprocal manner so as to follow the motion of the powder head and toselectively produce jets of a liquid binder material at selected regionsthereby causing the powdered material at such regions to become bonded.The binder jets are dispensed along a line of the printhead which ismoved in substantially the same manner as the dispensing head. Typicalbinder droplet sizes are about 15 to about 50 microns. The powder/binderlayer forming process is repeated so as to build up the restoration,layer by layer.

While the layers become hardened or at least partially hardened as eachof the layers is laid down, once the desired final shaped configurationis achieved and the layering process is complete, in some applicationsit may be desirable that the form and its contents be heated or cured ata suitably selected temperature to further promote binding of the powderparticles. In either case, whether or not further curing is required,the loose, unbounded powder particles are removed using a suitabletechnique, such as ultrasonic cleaning, to leave a finished restoration.

For effective use, the powder particles should be uniformly deposited ata relatively high rate, the rate being selected in accordance with theapplication for which the technique is used. For many usefulapplications the powder particles can preferably be packed at relativelyhigh densities, while in other applications the density may beconsiderably lower where restorations having greater porosity aredesired. Known techniques used in the fields of colloidal science andpowder dispersion chemistry can be used to provide the desired uniformdepositions of such powders at the required rates and densities. Thus,powders can be dispensed either as dry powders or in a liquid vehicle,such as in a colloidal dispersant or in an aqueous suspension. In thedry state, the desired compaction of particles can be achieved usingmechanical vibrating compaction techniques or by applying acousticenergy, i.e., either sonic or ultrasonic vibrations, to the depositedpowder or by applying a piezoelectric scraper to the deposited powder.

The ink-jet printing of the binder material should utilize droplets ofmaterials having shrinkage characteristics such that the dimensionaltolerances of the restoration being made are maintained upon hardeningthereof. While the binder solution must have a relatively high bindercontent, the viscosity thereof should be low enough so as to be able toflow through the printing head for deposit into the powder material. Thebinder material should be selected to penetrate the layer and to performits binding action relatively rapidly in each layer so that the nextlayer of powder particles can be subsequently applied thereto. Whenusing certain ink-jet technology the binder material may require atleast a minimum electrical conductivity, particularly when usingcurrently available continuous jet printing heads, for example, whichrequire enough conductivity to establish charge on the binder solutiondroplets as they are emitted from the head. Where conductivity cannot beestablished in the binder, as with certain organic solvents, forexample, the binder can be applied using drop-on-demand print heads.

The binder material may have a high binding strength as each layer isdeposited so that, when all the layers have been bonded, the componentformed thereby is ready for use without further processing. In othercases, it may be desirable, or necessary, to perform further processingof the restoration. For example, while the process may be such as toimpart a reasonable strength to the restoration which is formed, oncethe restoration is formed it can be further heated or cured to furtherenhance the binding strength of the particles. In some cases, the binderis removed during such heating or firing process, while in others, itcan remain in the material after firing. Which operation occurs dependson the particular binder material which has been selected for use and onthe conditions, e.g., temperature, under which the heating or firingprocess is performed. Other post-processing operations may also beperformed following the formation of the restoration. The rate at whicha ceramic, metal, plastic, or composite restoration can be made dependson the rates used to deposit the powder and to supply the binder liquid,and on the rate at which each bonded layer hardens as the layers aredeposited one on the other.

Any ceramic material having strength to withstand forces in the mouthmay be used herein. Preferably, the ceramic material is in particulateform. Examples of ceramic materials include, but are not limited toglass-ceramic materials, glass materials, high-strength ceramicmaterials such as alumina, zirconia, mullite, silica, spinel, tricalciumphosphate, apatite, fluoroapatite, hydroxyapatite and mixtures thereof.To enhance sintering, particles can be coated with silica, for exampleby treating with TEOS as described below. Many possible combinations ofpowder and binder materials can be selected in accordance with theinvention. For example, ceramic powders or ceramic fibers can be usedwith either inorganic or organic binder materials or with a metallicbinder material; a metal powder can be used with a metallic binder or aceramic binder; and a plastic powder can be used with a solvent binderor a plastic binder, e.g., a low viscosity epoxy plastic material. Otherappropriate combinations of powder and binder materials will occur tothose in the art for various applications.

The resulting color including but not limited to shade, translucency,and fluorescence, of the restoration is controlled by the pigments,opacifiers, fluorescing agents and the like, added to the powder bedcomponents as well as components delivered through nozzles. The printedmaterial that is used to bond successive layers can be a curable orremovable organic material. When a curable material is used, thepolymer-ceramic composite restoration results from the green body aftercuring is completed. Both natural and synthetic dispersants areavailable for these materials in organic vehicles. Organic dispersantshave been used in the ceramics industry and are typically polymericresins obtained form a variety of sources. They can be either watersoluble, such as cellulosic binders, as used in extrusion technology, orthey can be soluble in only volatile organic solvents, such as thebutyral resins, as used in tape casting technology. The latter watersoluble systems can be removed relatively quickly and seem particularlyuseful in the invention. Another example of a binder is a ceramicprecursor material such as polycarbosilazane.

Inorganic binders are useful in cases where the binder is toincorporated into the final component. Such binders are generallysilicate based and are typically formed from the polymerization ofsilicic acid or its salts in aqueous solution. An exemplary inorganicbinder which can be used is tetraethylorthosilicate (TEOS). Duringdrying, the colloidal silica aggregates at the necks of the matrixparticles to form a cement-like bond. During firing, the silica flowsand acts to rearrange the matrix particles through the action of surfacetension forces and remains after firing.

Composite materials for use in the invention include a polymeric matrixwith particulate or fiber filled components. The polymeric matrixelement of the fiber-reinforced and particulate-filled composites isselected from those known in the art of dental materials, including butnot being limited to polyamides, polyesters, polyolefins, polyimides,polyarylates, polyurethanes, vinyl esters or epoxy-based materials.Other polymeric matrices include styrenes, styrene acrylonitriles, ABSpolymers, polysulfones, polyacetals, polycarbonates, polyphenylenesulfides, and the like.

Preferred polymeric materials include those based on acrylic andmethacrylic monomers, for example those disclosed in U.S. Pat. Nos.3,066,112, 3,179,623, and 3,194,784 to Bowen; U.S. Pat. Nos. 3,751,399and 3,926,906 to Lee et al.; commonly assigned U.S. Pat. Nos. 5,276,068and 5,444,104 to Waknine; and commonly assigned U.S. Pat. No. 5,684,103to Jia et al., the pertinent portions of all which are hereinincorporated by reference. An especially preferred methacrylate monomeris the condensation product of bisphenol A and glycidyl methacrylate,2,2′-bis[4-(3-methacryloxy-2-hydroxy propoxy)-phenyl]-propane(hereinafter abbreviated “BIS-GMA”). Polyurethane dimethacrylates(hereinafter abbreviated “PUDMA”), triethylene glycol dimethacrylate(hereinafter abbreviated “TEGDMA”), polyethylene glycol dimethacrylate(hereinafter abbreviated “PEGDMA”), polycarbonate dimethacrylate(hereinafter abbreviated “PCDMA”) and ethoxylated bisphenol Adimethacrylate (hereinafter abbreviated “EBPADMA”) are alsocommonly-used principal polymers suitable for use in the presentinvention.

The polymer matrix typically includes polymerization initiators,polymerization accelerators, ultraviolet light absorbers, anti-oxidants,and other additives well known in the art. The polymer matrices may bevisible light curable, self-curing, dual curing, and vacuum, heat, andpressure curable compositions as well as any combination thereof. Thevisible light curable compositions include the usual polymerizationinitiators, polymerization accelerators, ultraviolet absorbers,fluorescent whitening agents, and the like. Preferred light curinginitiators include camphorquinone (CQ) and trimethyl benzoyl phosphineoxide (TPO). The heat curable compositions, which are generally filledcompositions, include, in addition to the monomeric components, a heatcure initiator such as benzoyl peroxide,1,1′-azobis(cyclohexanecarbonitrile), or other free radical initiators.The preferred fiber-reinforced polymeric matrix is a curable matrix,wherein light cure effects partial cure of the matrix, and final curingis by heat under controlled atmosphere.

The fiber-reinforced polymeric matrix may further comprise at least onefiller known in the art and used in dental restorative materials, theamount of such filler being determined by the specific use of thefiber-reinforced composite. Generally, no or relatively littleadditional filler is present in the polymeric matrix, i.e., up to thirtypercent by weight of the composite. Suitable fillers are those capableof being covalently bonded to the polymeric matrix itself or to acoupling agent that is covalently bonded to both. Examples of suitablefilling materials include but are not limited to those known in the artsuch as silica, silicate glass, quartz, barium silicate, strontiumsilicate, barium borosilicate, strontium borosilicate, borosilicate,lithium silicate, amorphous silica, ammoniated or deammoniated calciumphosphate and alumina, zirconia, tin oxide, and titania. Particularlysuitable fillers for dental filling-type materials prepared inaccordance with this invention are those having a particle size rangingfrom about 0.1-5.0 microns with a silicate colloid of 0.001 to about0.07 microns and may be prepared by a series of milling steps comprisingwet milling in an aqueous medium, surface etch milling and dry or wetsilanation. Some of the aforementioned inorganic filling materials aredisclosed in commonly-assigned U.S. Pat. No. 4,544,359 and No. 4,547,531to Waknine, the pertinent portions of which are incorporated herein byreference.

The particulate-filled polymeric matrix comprises at least one fillerknown in the art and used in dental restorative materials, the amount ofsuch filler being determined by the specific use of theparticulate-filled composite. Generally, from about 65 to about 85% byweight of a filler is present in the particulate-filled composite andpreferably, about 75 to about 83% by weight of the composite is fillerin combination with about 17 to about 35% by weight and preferably about20 to about 30% by weight and more preferably about 20 to about 26% byweight of the composite is unfilled heat curable dental resin materialwhich makes up the polymeric matrix. Suitable fillers are those capableof being covalently bonded to the polymeric matrix itself or to acoupling agent that is covalently bonded to both. Examples of suitablefilling materials include but are not limited to those known in the artsuch as silica, silicate glass, quartz, barium silicate, barium sulfate,barium molybdate, barium methacrylate, barium yttrium alkoxy(Ba₂Y(OR)_(x)), strontium silicate, barium borosilicate, strontiumborosilicate, borosilicate, lithium silicate, amorphous silica,ammoniated or deammoniated calcium phosphate, alumina, zirconia, tinoxide, tantalum oxide, niobium oxide, and titania. Particularly suitablefillers for dental filling-type materials prepared in accordance withthis invention are those having a particle size ranging from about0.1-5.0 microns with a silicate colloid of 0.001 to about 0.07 micronsand may be prepared by a series of milling steps comprising wet millingin an aqueous medium, surface etch milling and dry or wet silanation.Some of the aforementioned inorganic filling materials are disclosed incommonly-assigned U.S. Pat. Nos. 4,544,359 and 4,547,531 to Waknine, thepertinent portions of which are incorporated herein by reference.

Preferably, the particulate-filled composite comprises an inorganicfiller having an average particle size diameter of about 0.5 to about 5microns homogeneously dispersed in an organic polymerizable monomericmatrix comprising ethoxylated dimethacrylate which is set forth incommonly owned, copending application Ser. No. 08/998,849 filed Dec. 29,1997, now U.S. Pat. No. 5,969,000, which is hereby incorporated byreference. In addition, a relatively small amount of fumed silica isalso predispersed within the monomeric matrix. The inorganic fillerprimarily comprises an X-ray opaque alkali metal or alkaline earth metalsilicate such as lithium alumina silicate, barium silicate, strontiumsilicate, barium borosilicate, strontium silicate, barium borosilicate,strontium borosilicate, borosilicate, as well as the aforementionedmaterials. For purposes of illustration, and as the preferred silicatespecies, barium borosilicate will hereinafter be employed as beingtypical of the alkali metal or alkaline earth metal silicates which canbe suitable employed in the present invention. The barium borosilicateexhibits an index of refraction close to that of the organic monomericmatrix in which it is dispersed. The filler can additionally contain arelatively small amount of borosilicate glass which imparts greatercompressive strength to the resulting composite and enhances thetranslucency thereof thereby enabling better blending of the restorativematerial with the adjacent teeth. In addition, the presence of theborosilicate glass helps narrow the gap in the mismatch of refractiveindices between the barium borosilicate inorganic fiber phase and theorganic monomeric matrix.

Details of the preparation of the inorganic filler, which comprises amixture of from about 5 to about 20% by weight of borosilicate glass andform about 80 to about 95% by weight barium borosilicate, and has anaverage particle size diameter of from about 0.5 to about 5 microns, canbe found in the aforementioned U.S. Pat. Nos. 4,544,539 and 4,547,531.

The reinforcing fiber element of the fiber-reinforced compositepreferably comprises ceramic, glass, carbon, graphite, polyaramid, orother fibers or whiskers known in the art, such as polyesters,polyamides, and other natural and synthetic materials compatible withthe polymeric matrix. Some of the aforementioned fibrous materials aredisclosed in commonly assigned copending U.S. patent application Ser.Nos. 08/907,177, 09/059,492, 60/055,590, 08/951,414, now U.S. Pat. No.6,013,694, and U.S. Pat. Nos. 4,717,341 and 4,894,012 all which areincorporated herein by reference. The fibers may further be treated, forexample, chemically or mechanically etched and/or silanized, to enhancethe bond between the fibers and the polymeric matrix. The fiberspreferably take the form of long, continuous filaments, although thefilaments may be as short as 0.1 to 4 millimeters. Shorter fibers ofuniform or random length might also be employed. Preferably, the fibersare at least partially aligned and oriented along the longitudinaldimensions of the wire. However, depending on the end use of thecomposite material, the fibers may also be otherwise oriented, includingbeing normal or perpendicular to that dimension.

As set forth above, in all procedures herein, metal powder may be usedto form the dental restoration or model or other desired product to bemanufactured in accordance herein. The metal powder may be provided asmetal alone, in any know form such as in powder or molten form and maybe used in combination with a binder. If a binder is used, thepowder/binder mixture comprises from about 50 to about 99 percent powderand from about 1 to about 50 percent binder, and preferably from about70 to about 99 percent powder and from about 1 to about 30 percentbinder, and more preferably from about 90 to about 99 percent powder andfrom about 1 to about 10 percent binder. Most preferably, the powder ispresent in about 95% by weight and the binder is present in about 5% byweight.

The metal powder may comprise one or more precious metals, non-preciousmetals and alloys thereof. Preferably, the metal powder is a high fusingmetal and preferably, the metal powder comprises a non-oxidizing metal.More preferably, the metal powder is selected from one or more of gold,platinum-Group metals, silver and alloys thereof whereby the alloys maycomprise one or more of the metals in combination with one another orwith a different metal, such as copper, iridium, rhodium, palladium,indium, tin, gallium and mixtures thereof. One preferred alloy comprisesabout 85 to about 99% Au, 0 to about 15% Pt, and 0 to about 15% of oneor more of Ag, Pd, Rh, Ir, In, Ru, and Ta.

The particle size of the metal powder is not limited to any specificsize. The metal powder may comprise a multimodal particle sizedistribution to achieve high density during sintering. The multimodalparticle powder comprises larger or coarse particle size powder incombination with a smaller or fine particle size powder. The averagesize of the coarse particle powder can be about 25 to about 35 microns,with the majority of the particles exhibiting diameters in the rangefrom about 5 to about 100 microns and preferably with the maximum sizeno greater than about 44 microns (−325 mesh) to about 50 microns (−270mesh). The fine particle size is less than about 5 microns andpreferably less than about 2 microns. The coarse particles are presentin an amount in the range of about 85 to about 95% by weight and thefine particles are present in an amount in the range of about 5 to about15% by weight of the powder.

In some applications, it may be preferable that the binder hardenrelatively rapidly upon being deposited so that the next layer ofparticles placed on a surface of the previous layer is not subject toparticle rearrangement due to capillary forces. Moreover, a hardenedbinder is not subject to contamination from solvents which may be usedin powder deposition. In other cases, it may not be necessary that thebinder be fully hardened between layers and a subsequent layer of powderparticles may be deposited on a previous layer which is not yet fullyhardened.

The number of restorations printed simultaneously is essentially limitedby the size of the powder bed, number of nozzles and the ability torecognize and sort different restorations. To facilitate the latteroperation, the robotized device can be used to pick up and sortdifferent restorations.

It is an essential part of the present invention that componentscreating and/or modifying color, translucency, biocompatibility,mechanical properties (strength, fracture toughness and wear) andperceived shape are contained in the powder bed and/or delivered throughnozzles. This offers a unique advantage in creating esthetics (colors,shapes) and structure (functionally gradient structures). Techniquessimilar to water-marks are used to create interference colors,opalescence and fluorescing effects. Other techniques are used to createperceived geometry similar to techniques used in sculpture to createimpressions of the face that is perceived as a full-bodied face alwayslooking at the observer from any angle of view.

In another embodiment of the present invention, moldable articles arefabricated in the form of feed stock (wire or filament) that is formedinto the required shape of a dental restoration using a fused depositionmodeling machine such as FDM2000 available from Stratasys Inc., EdenPrairie, Minn. The software used accounts for the anticipated shrinkage.The free-standing shaped article is then sintered to full density. Thismethod can only be used for powder such as alumina or zirconia which iscapable of isotropic shrinkage during sintering. U.S. Pat. No. 5,900,207is directed to solid free form fabrication methods which is herebyincorporated by reference.

In another embodiment of the present invention, a slurry or paste of apolymer or ceramic powder is mixed with a carrier formed into a copingof a multi-layered final shape of a dental restoration using a machinesimilar to a fused deposition modeling machine. This machine emits orsprays beads of slurries as opposed to a fused deposition modelingmachine which emits liquefied thermoplastic materials. Examples ofbinder materials include curable organic materials such as mixtures ofmonomers or organic materials that are burned out prior to sintering.The shrinkage and setting of the materials are taken into account byoversizing the green body prior to sintering/curing.

In yet other embodiments of the present invention, other solid free-formfabrication techniques are used to make dental restorations fromceramic, glass-ceramic, metal or composite materials.

In still another embodiment herein, SFF methods are used to provide onlya skeleton of a dental restoration, e.g. a structure withinterpenetrating porosity or a reticulated (cellular, honeycomb) body.This body is later infiltrated with “biological soup” containing cellcultures or peptides that can yield in-vitro grown materials similar tohuman tooth or bone tissues also known as biomimetic materials. Forexample, this infiltration media can contain biomimetically grown dentalenamel crystals as described in U.S. Pat. No. 4,672,032 by Slavkin etal, which is hereby incorporated by reference. Another example ofinfiltration media is cultured periosteal cells as described in U.S.Pat. No. 5,700,289 to Breitbart et al.

In still yet another embodiment herein, rapid prototyping methods areused to form a “negative” or an impression of the tooth, teeth, orportion of the patient's mouth to be restored. As standard procedure,the dentist prepares the patient's tooth or teeth to be restored.Thereafter, the dentist takes an impression of the teeth. Alternatively,the dentist may scan the patient's teeth with a scanning device toobtain data that represents the shape of the patient's teeth. Scanningcan be performed on a patient's teeth, a master die, a working die, or awax-up of a dental restoration. If an impression is taken, it istypically sent to a laboratory where a master die is made, or otherwise,the scanned data is sent to the laboratory or milling center forpreparation of the restoration.

In accordance herein, if an impression is taken, it is scanned with ascanning device to obtain data representative of the shape of theimpression. With the data obtained from the scanning of the impressionor the scanning of the patient's mouth, a “negative” or shell materialis prepared by a rapid prototyping process. The material used to preparethe shell is any material capable of withstanding the weight and forceof a duplicate master or refractory model material including, but notlimited to polymeric materials including, but not limited to waxes,nylons, plastics, rubber materials and other thermoplastic materials.Also, plaster and composite materials are other examples that may beuseful herein. Examples of waxes include but are not limited to paraffinwaxes, microcrystalline waxes, synthetic hydrocarbon waxes, oxidizedpolyethylene waxes and combinations of the foregoing. It is preferablethat the wax has a modulus of elasticity of below about 10 GPa and morepreferably below about 5 GPa. It is preferable that the wax have flowcharacteristics according to American Dental Association (ADA)Specification No. 4 for Type I and Type II waxes. At 45° C., the Type Iand Type II waxes have a minimum flow percentage of 70% and a maximumflow percentage of 90%. If the shell is used as a wax pattern forcasting or pressing restorations, it should burn out cleanly duringburn-out procedures. It is important that waxes used are not too brittleand do not undergo dimensional changes under ambient conditions.

The aforementioned techniques and procedures discussed above in regardto the rapid prototyping of dental restorations apply hereto to therapid prototyping of shells and dies and are hereby incorporated byreference. The techniques used to form the shell and die may includethree-dimensional printing, selective area laser deposition or selectivelaser sintering (SLS), electrophoretic deposition, robocasting, fuseddeposition modeling (FMD), laminated object manufacturing (LOM),stereolithography and photostereolithography. U.S. Pat. Nos. 5,340,656,5,490,882, 5,204,055, 5,518,680, 5,490,962, 5,387,380, 5,700,289, and4,672,032 are directed to solid free-form fabrication methods andtechniques and are hereby incorporated by reference.

The design of the shell is carried out by a CAD device which uses atleast two inputs: (1) the digital image taken optically directly from amouth of the patient (optical impression) or created by digitizing theimpression/die by contact or by an optical digitizer; and (2) a libraryof teeth shapes and forms. CAD devices assure both natural-like shapeand proper function of the shell. Both optical and contact digitizersproviding input (1) above are described in the literature and some ofthem are commercially available. The specific techniques may requireadditional software to build the shape according to the CAD file.

The data from the CAD file is input into the rapid prototyping devicesuch as a fused deposition modeling machine. A continuous filament orrod of a polymeric material such as wax is introduced into a channel ofa nozzle inside which the rod/filament is driven by a motor andassociated rollers to move like a piston. The front end, near a nozzletip, of this piston is heated to become melted. The rear end or solidportion of this piston pushes the melted portion forward to exit throughthe nozzle tip. The nozzle is translated under the control of a computersystem in accordance with previously sliced CAD data to trace out athree-dimensional shell point by point and layer by layer. The CAD datamay be modified to provide a shell having a thickness sufficient towithstand the weight and pressure of refractory die material that willbe poured into the shell for fabrication of a model or die. Thestructure of the shell may be solid or reticulated. Preferably, the areaof the shell closest to the internal surface of the shell exhibits asolid structure or form and the area further from the internal surfaceexhibits a reticulated or honeycomb structure. If the shell is to beused as a wax pattern for casting, it does not require bulking. Itshould have the dimensions of the restoration to be fabricated.

The shell or full model of the restoration obtained by rapid prototypingtechniques is then used to fabricate a master model and/or a workingdie, both of which are used in the fabrication of dental restorations.Alternatively, as discussed, the shell can be used as a wax pattern forcasting or pressing restorations. The technique used is commonly knownas the lost-wax process. The shell, as the wax pattern, is invested in arefractory investment material. The wax pattern is “burned out” to forma cavity in the shape of a coping. Ceramic, metal, polymeric or othersimilar material is then injected, vibrated, poured, pressed, orinserted by similar means into the cavity to form the dentalrestoration. The ceramic, metal or polymeric material may include anymaterials known in the field of dentistry including the aforementionedmaterials discussed above.

The shell or full model of the restoration, produced by techniquesdiscussed herein, obviates the need for a dentist to send an impressionto a dental laboratory, saving time and labor, and thereby expeditingthe process of manufacturing a dental restoration. After manufacture ofthe shell by rapid prototype techniques, a refractory die material orgypsum material is poured into the shell to provide a model or workingdie. Alternatively, the die or working model may be formed by rapidprototyping processes as discussed herein from refractory, ceramic,glass, metal, polymeric and composite materials or from known millingprocesses. Examples of metal materials for manufacture of the dieinclude, but are not limited to, molybdenum, nickel or alloys comprisingnickel or molybdenum. Commercially available metals include RexilliumIII from Pentron Corporation, Hastelloy from Haynes International, Inc.and Inconel 600 from Inco Alloys International, Inc.

Alternatively, a substrate, die or mold is designed from the digitaldata obtained from a patient's tooth or teeth. The die or mold may beenlarged to accommodate for the shrinkage that occurs in the ceramicmaterial that is applied to the die or mold. The enlarged die or mold orprototype may be fabricated of any material able to withstand the weightof the dental material applied thereto including, but not limited to,wax, paraffin, rubber, plastic, polymeric material, thermoplasticmaterial, thermosetting material or a light curable resin material. Thelight curable resin may be curable by visible or UV light. Examples ofwaxes include, but are not limited to, paraffin waxes, microcrystallinewaxes, synthetic hydrocarbon waxes, oxidized polyethylene waxes andmixtures thereof. Examples of light curable resins include, but are notlimited to, acrylic, epoxy, silicone resins or monomers or mixturesthereof.

A dental material, such as ceramic, composite, or alloy material, isapplied or pressed onto the die to provide a dental restoration.

It is preferred that ceramic particulate material is used. Applicationof the ceramic particulate material onto or into the mold or die mayinclude gel casting, slip casting, slurry casting, pressureinfiltration, pressure casting, direct coagulation, dipping, colloidalspray deposition, electorphoretic deposition, injection molding,extrusion, heat pressing, hot pressing, hot casting, centrifugalcasting, gravity casting.

The mold or die may be fabricated of any known material including, butnot limited to, die stone, clay, plaster of paris, gypsum, silica,leucite, zirconia, hafnia, zirconia, alumina, magnesia, zircon,aluminosilicate, cordierite, mica, silicon nitride, silicon carbide,silica-alumina-nitrides, mullite, garnet, or mixtures thereof.

The ceramic particulate material may be in the form of a suspension,slurry, slip, gel, pellet, or feedstock.

In accordance with an embodiment herein, a ceramic material that is inits green state or that has been partially sintered or soft-sintered,may be milled, machined, or formed by solid free form fabricationmethods, into a coping or framework. Partial or soft sintering comprisessintering to less than full density, preferably less than about 92%,more preferably less than about 80%, and most preferably less than about75%. Partial or soft sintering produces a product having about 8 toabout 25 percent porosity, making it easier to mill.

Ceramic materials useful herein include high strength ceramic materialssuch as, but not limited to alumina, zirconia, hafnia, silicon nitride,silicon carbide, silica-alumina-nitrides, mullite, various garnets etc.and porcelain materials such as commercially available OPC®3G™ porcelainand OPC® porcelain, both available from Jeneric/Pentron Inc.,Wallingford, Conn., and commercially available Empress™ porcelain andEmpress II™ porcelain, both available from Ivoclar North America,Amherst, N.Y. The porcelain materials may include leucite, lithiumdisilicate, mullite or mica as the crystal phase.

Milling procedures include those known in the art and methods andequipment described in U.S. Pat. Nos. 4,937,928, 5,910,273, 4,575,805,and 4,663,720 and are hereby incorporated by reference. Examples ofcommercially available CAD/CAM systems include the Cerec™ systemavailable from Sirona™ USA, Charlotte, N.C., and the Pro 50™ systemavailable from Cynovad™, Quebec City, Canada. Solid free formfabrication methods include those described herein.

The coping or framework is formed from the same data that was used toform the die, i.e., data obtained from the mouth or from an impressiontaken, or data taken from the die itself, so that the coping orframework closely matches the contour of the die and fits appropriatelyon the die. After the coping or framework has been formed, it is placedon the die and the coping or framework is fully sintered to its finaldensity. As the coping or framework is sintered to its final density,porosity is reduced and shrinkage occurs. The coping or framework issupported by the die, therefore there is little chance of warpage. Thecoping or framework will shrink onto the die, and will not warp or flareup.

Dental restorations manufactured using this process include, but are notlimited to, orthodontic appliances, bridges, space maintainers, toothreplacement appliances, splints, crowns, partial crowns, dentures,posts, teeth, jackets, inlays, onlays, facing, veneers, facets,implants, abutments, cylinders, and connectors.

Alternatively, after the model or die is prepared, a framework, copingor other dental appliance is designed using computer assisted designsoftware. The software used to design the dental appliance is any knownavailable software, preferably that software which is supplied with thescanning machine, or that which is compatible with the scanning machine.The framework is designed and saved as a stereolithography (.STL) file.The .STL file is transferred to a computer interfaced with a rapidprototyping machine such as the Perfactory™ Mini available from EnvisionTechnologies GmbH LLC. The machine uses photostereolithography to buildthe substrate for the framework based on the .STL file. Thesubstrate/model/die is built using light curable (by visible or UVlight) material, which may be in the form of a suspension, emulsion ormixture comprising any known material able to withstand the subsequentcoating or deposition process, including but not limited to, gypsum,silica, leucite, zirconia, hafnia, zirconia, alumina, magnesia, hafnia,zircon, aluminosilicate, cordierite, mica, silicon nitride, siliconcarbide, silica-alumina-nitrides, mullite, garnet, or mixtures,composites, polymers, plastics, metals, alloys and mixtures thereof.

In the preferred DLP method, the digital pixel-based mask is projectedonto the layer of light curable material and causes selectivepolymerization of this material in the areas corresponding to pixelsthat are illuminated, whereas the areas corresponding to dark pixelsremain uncured. Each group of illuminated pixels gives rise to thespecific cross-section of the article built layer by layer. The processof photopolymerization can be aided by concurrent or subsequent actionof other types of radiation such as heat (infrared radiation) and/ormicrowave radiation to strengthen the substrate.

After the substrate is built, the framework is formed thereon,preferably by gel casting, slip casting, slurry casting, pressureinfiltration, dipping, colloidal spray deposition or electrophoreticdeposition. Materials useful for the fabrication of the frameworkinclude, but are not limited to, any ceramic, polymeric, or metalmaterial able to withstand the forces in the mouth, including but notlimited to, zirconia, yttria, hafnia, alumina, ceria, magnesia, titania,silicon nitride, silicon carbide, silica-alumina-nitride, mullite,garnets, porcelain, or mixtures thereof. It is preferable that ceramicparticulate material is used. It can be in the form of solid solutions,agglomerates, complexes or the like. A binder may be included with theceramic material for maintaining the shape of the form prior tosintering. Binders may include but are not limited to inorganic andorganic binders, or mixtures thereof. Organic binders include, but arenot limited to, polyvinyl pyrrolidine, polyvinyl alcohol, polyvinylacetate, polyvinyl chloride, polyvinyl butryal and polystyrene, ormixtures thereof. Inorganic binders include, but are not limited to,magnesium oxide, ammonium phosphate, colloidal silica, calcium sulfate,magnesium phosphate, alkaline silicates, silica hydrosol, colloidalclays, or mixtures thereof.

After the framework is formed it is sintered at required times andtemperature to provide a high strength dental restoration.

Reference is made to FIGS. 1 through 6. FIG. 1 depicts a cross-sectionalview of a shell 10 that has been formed by a rapid prototyping method asdescribed herein. Shell 10 was formed from data retrieved by the dentistduring the scanning procedure of the patient's tooth. The data was inputinto a rapid prototyping device to obtain shell 10. A die or model 20shown in FIG. 2 was then prepared by filling shell 10 with refractorymaterial known in the art. FIG. 3 is a cross-sectional view of shell 10with die 20 formed therein. FIG. 4 shows a plug 40 that may befabricated of a wax, plaster, plastic or rubber material. Plug 40 may beused to maintain the refractory material in place during setting afterit has been poured into shell 10. FIG. 5 depicts a cross-sectional viewof a shell 50 used in a lost wax process. Shell 50 is made using rapidprototyping techniques, based on information scanned from the patient'smouth or the impression taken from the patient's mouth. Shell 50 isshown attached to sprue 52 and is encased in investment material 54.During the burn-out procedure, shell 50 and sprue 52 are burned away,leaving a space 60 as shown in FIG. 6, for casting of metal or pressingof a ceramic.

In another embodiment herein, rapid prototyping techniques are used tofabricate master models and working dies or models that are used in thefabrication of dental restorations. Techniques and procedures discussedabove in regard to the rapid prototyping of dental restorations andshells apply hereto to the rapid prototyping of master models andworking models and are hereby incorporated by reference. The techniquesused to form the models and dies may include three-dimensional printing,selective area laser deposition or selective laser sintering (SLS),electrophoretic deposition, robocasting, fused deposition modeling(FMD), laminated object manufacturing (LOM), stereolithography,photostereolithography and digital light processing (DLP). U.S. Pat.Nos. 5,340,656, 5,490,882, 5,204,055, 5,518,680, 5,490,962, 5,387,380,5,700,289, and 4,672,032 are directed to solid free-form fabricationmethods and techniques and are hereby incorporated by reference.

Similar to the aforementioned techniques used to form shells and dentalrestorations, data received from scanning the patient's mouth or theimpression of the patient's mouth is used to fabricate models usingsolid free-form fabrication methods. Materials useful for themanufacture of models include investment materials. Typical investmentmaterials include gypsum for low temperature applications, and arefractory filler, such as silica in the form of cristobalite, quartz,or a mixture of the two, leucite, zirconia, hafnia, zircon, alumina,magnesia, zircon, aluminosilicate, cordierite, mica, silicon nitride,silicon carbide, silica-alumina-nitrides, mullite, garnet, or mixturesthereof, in combination with a binder, for high temperatureapplications. Binders may include but are not limited to inorganic andorganic binders, or mixtures thereof. Organic binders include, but arenot limited to, polyvinyl pyrrolidine, polyvinyl alcohol, polyvinylacetate, polyvinyl chloride, polyvinyl butryal and polystyrene, ormixtures thereof. Inorganic binders include, but are not limited to,magnesium oxide, ammonium phosphate, colloidal silica, calcium sulfate,magnesium phosphate, alkaline silicates, silica hydrosol, colloidalclays, or mixtures thereof. The investment material is fed to the solidfree-form apparatus which interprets the scanned data and produces athree-dimensional model with the investment material.

Alternatively, the model may be formed of a thermoplastic material asdescribed above for the use of shells, and the wax model may beduplicated using standard techniques.

For all purposes and materials used herein, the hardening or curing stepmay involve gelation, heating, cooling, or the application to promotethe integrity of the solid free-form structure.

FIG. 7 shows examples of models and dies which are created by CADsoftware and thereafter produced by rapid prototyping. A full model ofteeth 70, a single coping 72 and a bridge unit 74 are shown. FIG. 8shows a series of copings 80 that have been produced by rapidprototyping and are ready for application of a ceramic, polymeric, ormetal material thereon.

FIG. 9 shows a series of copings 90 prior to placement in suspension ofcharged particles 92. The suspension may include any of the materialsmentioned above for fabrication of the restoration including but notlimited to high strength ceramic materials. The copings 90 are attachedto copper electrodes 94. The process used is known as ElectrophoreticDeposition (EPD) which is an electroforming process in which chargedparticles dispersed in a stable suspension are driven by the appliedelectric field to move towards an oppositely charge electrode, uponwhich they ultimately deposit, to build up a particulate coating. Thetechnique is used herein to fabricate green ceramic bodies and coatingswith different shapes for applications ranging from ceramic/ceramic andmetauceramic composites to thin/thick film coatings for electronicdevices. This processing technique is especially useful for thepreparation of uniform particulate coatings with high green densities(45%-75%) and controlled thickness.

FIG. 10 illustrates an alternative method for applying material onto thesubstrate to form the coping and shows a slip bath 100 of ceramicmaterial in combination with a binder into which the series of copings102 are inserted for application of the slip.

After the application of the ceramic or other material, the coping iscured or sintered to provide the dental restoration. The restoration ispreferably veneered with a porcelain or composite material to providethe finished restoration. The porcelain should have a coefficient ofthermal expansion up to about ±2×10⁻⁶/° C. of the CTE of the sinteredceramic particulate material that is used to manufacture the core of thedental article or restoration.

The following examples illustrate the practice of the present invention.

Example 1

Filament is prepared from Investment Casting Wax (ICW06, Stratasys) andthermoplastic ABS (P400, Stratasys) and equiaxed alumina powder of 5 to10 microns particle size. The binder content is about 30 volume percent.

Using a CAD/CAM device and digitizer manufactured by CAD/CAM Ventures(Irving, Tex.), the model of a tooth preparation is digitized and theobtained CAD file is used in conjunction with an FDM2000 fuseddeposition modeling machine available from Stratasys Inc. (Eden Prairie,Minn.). Using the filament containing equiaxed alumina powder in athermoplastic matrix, single and multiunit dental restorations areformed and then subjected to binder-removal and soft-sintering cycles.The resulting porous preforms are infiltrated with glass using materialssupplied by Vita Zahnfabrick (Bad Sackingen, Germany) and glassinfiltration techniques used for Vita In-Ceram Alumina restorations.

Example 2

The same CAD file as used in Example 1 is used in conjunction with athree-dimensional printing machine such as the Z402 System availablefrom Z Corporation (Mass.) to print on ceramic powder and on metalpowder separately. The same powder-binder mixture used above is usedherein as the powder layer. A binder mixed with finely dispersedpigments is printed on the powder layer. Successive layers are depositedto form a dental restoration based on the CAD file. After therestoration is fully formed, the binder is burned out and glass is theninfiltrated into the interstices. The pigment is retained ininterstitial sites between the alumina particles to impart a shade tothe composite.

Example 3

Using a CAD/CAM device and digitizer manufactured by CAD/CAM Ventures(Irving, Tex.), the model of a tooth preparation is digitized and theobtained CAD file is used to manufacture a shell. The CAD file ismodified to provide a thickness in the shell great enough to support andwithstand the refractory materials. The thickness of the shell variesfrom about 0.5 to about 10 mm in thickness. The shell produced isthinner near the margin and thicker near the apex. This information isfed into a computerized liquid wax dispensing machine. A green injectionwax available from Romanoff Inc. is injected into the machine. The waxis delivered as tiny beads in liquid state that solidify shortly afterdispensing. The internal surface of the shell is smooth. The supportstructure of the shell is in the form of a solid or void-containingstructure, such as a honeycomb structure. Polyvest refractory materialavailable from WhipMix corporation is poured into the shell and sets.After setting, a duplicate refractory die is retrieved and used forfurther processing of materials.

Example 4

An optical scanner, ZFN D-21, available from ZFN (ZahntechnischesFraszentrum Nord GmbH & Co. KG (Warin, Germany) is utilized to scanmaster models (dies) made from impressions comprising preparations forbridges and crowns. 3D CAD software provided with a ZFN D-21 scanner isused to design frameworks and copings corresponding to these mastermodels (dies). 3D CAD files (solid models) of these frameworks andcopings are enlarged using the linear shrinkage coefficientcorresponding to the anticipated sintering shrinkage of the materials ofthe present invention, saved as stereolithography (.STL) files andtransferred to a computer interfaced with an RP (Rapid Prototyping)machine such as Perfactory® Mini available from Envision TechnologiesGmbH (Marl, Germany). This machine utilizes an approach known asphoto-stereolithography to build 3D objects from a light curable resin.Fifteen units are built at the same time layer by layer with anindividual layer thickness of about 50 microns. Individual units areseparated, attached to copper wire electrodes and coated with conductivesilver paint (silver lacquer) available from Gramm GmbH or WielandDental+Technik GmbH & Co., KG (Pforzheim/Germany). An electroformingunit, such as, AGC® Micro Plus (Wieland Dental+Technik GmbH & Co. KG) isused to deposit a rigid green layer of zirconia in the form ofyttria-stabilized zirconia polycrystals (YTZP) from an ethanol-basedsuspension as described in Example 3 of U.S. Pat. No. 6,059,949, whichis hereby incorporated by reference. An electroforming suspension isprepared by suspending commercial YTZP powder grade available as TZ-3Y-Efrom Tosoh USA, Inc. (USA representative of Tosoh Corporation, Tokyo,Japan) in pure ethanol with the addition of 0.05% vol. acetyl acetonedispersant and 0.1% vol. of 5% wt. of a polyvinyl butyral binder (PVB)in pure ethanol. The average thickness of the electrophoretic coating is0.5-0.6 mm. Following electroforming of the powders on the substrates,sintering is carried out in a Deltech furnace at a rate of 1° C./min to700° C. for approximately 2 hours followed by a rate of 1° C./min. to1400° C. for approximately 2 hours. Resin substrates are completelyburned out during the 2 hour soak at 700° C.

Example 5

An optical scanner, ZFN D-21, available form ZFN (ZahntechnnischesFraszentrum Nord GmbH & Co. KG (Warin, Germany) is utilized to scanmaster models (dies) made from impressions comprising preparations forbridges and crowns. 3D CAD software provided with a ZFN D-21 scanner isused to design frameworks and copings corresponding to these mastermodels (dies). 3D CAD files (solid models) of these frameworks andcopings are enlarged using the linear shrinkage coefficientcorresponding to the anticipated sintering shrinkage of the materials ofthe present invention, saved as .STL files and transferred to a computerinterfaced with an RP (Rapid Prototyping) machine, such as thePerfactory® Mini machine available from Envision Technologies GmbH(Marl, Germany). This machine utilizes an approach known asphotostereolithography to build 3D objects from a light curable resin.In this example, resin is filed with 30 vol % of a water soluble salt.Fifteen units are built simultaneously, layer by layer with eachindividual layer having a thickness of about 50 microns. Following rapidprototyping, the platform (shown in FIG. 10) having all substrates stillattached to it, is immersed into water to wash out salt to createinterconnected porosity in the substrates. Zirconia slip is preparedfrom commercially available powder such as TZ-3YS-E from Tosoh USA Inc.(USA representative of Tosoh Corporation, Tokyo, Japan). Based on thetotal weight of the dry YTZP powder, Duramax™ B-1000 binder in an amountof 3% by weight and D-3005° dispersant in an amount of 0.4% by weight,both available form Rohm and Haas, are used to make aqueous slipcontaining 65 volume percent of solids. Copings are formed bysimultaneous dipping of all the substrates still attached to theplatform into the slip. Sintering is carried out in a Deltech furnace ata rate of about 1° C./min to about 700° C. and held for approximately 2hours followed by heating at a rate of about 1° C./min. to about 1500°C. and held for approximately 2 hours. Resin substrates are completelyburned out during the 2 hour soak at 700° C.

Example 6

Substrates are fabricated as described in examples 4 and 5 above.Copings are formed simultaneously by sequential dipping andaging/drying. An alkaline casting slip with a pH of about 9-9.5 isprepared by adding 350 g zircon oxide (PSZ with 6 mole % Y₂O₃Rhone-Poulenc, France) to a solution of 1.75 g acetic acid ethyl esterand 1.4 grams of an ammonium polyacrylate solution (Darvan C,Wanderbilt, USA) in 49.0 grams of deionized water. After deagglomerationand degassing, 500 units esterase (EC 3.1.1.1) are added as a solutionwith 2000 units/ml to the slip (viscosity ca. 500 mPas). The copings arethereafter sintered as in Example 5.

Example 7

An optical scanner, ZFN D-21, available from ZFN (ZahntechnischesFraszentrum Nord GmbH & Co. KG (Warin, Germany) is utilized to scanmaster models (dies) made from impressions comprising preparations forbridges and crowns. 3D CAD software provided with a ZFN D-21 scanner isused to design frameworks and copings corresponding to these mastermodels (dies). 3D CAD files (solid models) of these frameworks andcopings are enlarged using the linear shrinkage coefficientcorresponding to the anticipated sintering shrinkage of the nanozirconiamaterials of the present invention, saved as stereolithography (.STL)files and transferred to a computer interfaced with an RP (RapidPrototyping) machine such as a Perfactory® Mini available from EnvisionTechnologies GmbH (Marl, Germany). This machine utilizes aphotostereolithography process also known as digital light processing(DLP) to build 3D objects from a light curable resin. Fifteen units arebuilt simultaneously layer by layer with each individual layer having athickness of about 50 microns. Individual units are separated and moldedin liquid silicone rubber, such as commercially available Silastic® MRTV Silicone Rubber (from Dow Corning Corporation) which is castable andeasily demolded after curing of the PSZ to produce negative molds forlow-pressure injection molding. It should be noted that instead of usingsilicone negative molds, the molds for Low-Pressure Injection Molding(LPIM) (also known as hot casting with a Peltsman Unit) can be designedand fabricated directly using the Perfactory® Mini RP machine and thesupplied software.

Feedstock for injection molding containing submicron zirconia powder isprepared from a binder comprised of 75 wt % of paraffin wax (meltingpoint of 49°-52° C.), 10 wt % of polyethylene wax (melting point of80°-90° C.), 10% of carnauba wax (melting point of 80°-87° C.), 2 wt %of stearic acid (melting point of 75° C.) and 3 wt % of oleic acid(melting point of 16° C.) readily available from a number of suppliers.Commercially available TZ-3YS-E powder from Tosoh USA Inc. (USArepresentative of Tosoh Corporation, Tokyo, Japan) is used. The mixingis done directly in a low pressure molding (LPM) machine, (Model MIGL-33available from Peltsman Corporation, Minneapolis, Minn.) at atemperature of 90° C. The feedstock mixture is comprised of about fiftypercent (50%) by volume of a binder. Once the feed stock mixture isthoroughly mixed, it is injected into the cavity of the silicone rubbermolds at a pressure of approximately 0.4 MPa and at a temperature ofapproximately 90° C. The injection-molded green part is then demoldedfrom the silicone mold, which is done easily due to elasticity of thesilicone. Green densities of approximately 50% were achieved. The greenbodies were debinderized and sintered to nearly full density asdescribed in Example 5 above.

Example 8

Feedstock for injection molding containing submicron zirconia powder isprepared from a binder comprised of 75 wt % of paraffin wax (meltingpoint of 49°-52° C.), 10 wt % of polyethylene wax (melting point of80°-90° C.), 10 wt % of carnauba wax (melting point of 80°-87° C.), 2 wt% of stearic acid (melting point of 75° C.) and 3 wt % of oleic acid(melting point of 16° C.) readily available from a number of suppliers.TZ-3YS-E powder, available from Tosoh USA Inc. (USA representative ofTosoh Corporation, Tokyo, Japan) is used. The mixing is done in aKitchenAid Professional 5 mixer (St. Joseph, Mich.) in a bowlcontinuously heated to 90° C., which is above the melting point of thebinder. Heating is achieved using a high temperature heat tape availablefrom McMaster-Carr (New Brunswick, N.J.). The heat tape is wrappedaround the mixer bowl to provide heat to the bowl. After cooling to roomtemperature, the resulting mix is crushed into powder to a 60 mesh (250microns) particle size using a mortar and pestle. This powder is thenready for injection into the cavity of a mold. Additionally, the mix canbe cast into pellets by pouring into a metal “clam-shell” mold, whilestill in the molten state.

Previously acquired stereolithography (*.STL) files of bridge frameworksand crown copings were sent to microTEC, Bismarckstrasse 142 b 47057Duisburg, Germany) for production of the enlarged replicas usingRMPD®-mask technology via a toll rapid prototyping service availablethrough microTEC's website. The replicas were fabricated in a layerthickness of twenty five microns (25 microns) from photo-curable resin.

The resulting replicas are invested in Universal™ Refractory Investment(available from Pentron® Laboratory Technologies, LLC, Wallingford,Conn.). After the investment has hardened, the resin replicas inside areeliminated by placing it into a preheated furnace thereby burning offthe resin, resulting in a mold cavity for forming the dental article.The injection molding feedstock, in free-flowing granule or pellet form,as described above, is then placed into the investment mold assembly,which is then transferred into the pressing unit. It is pressed into theinvestment ring using an AutoPressPlus® furnace (Pentron LaboratoryTechnologies, LLC, Wallingford, Conn.) having an external aluminaplunger. Pressing is done at approximately 90° C., and after cooling thepressed green part is then carefully divested by sand-blasting withglass beads at a pressure of 15 psi and the plunger and mold aredisposed of. Green densities of approximately 50% were achieved. Thegreen bodies were debinderized and sintered to nearly full density asdescribed in Example 5 above. Some of the sintered copings and bridgeframeworks were layered with 3G® porcelain (available from (Pentron®Laboratory Technologies, LLC, Wallingford, Conn.) to demonstrate thefinishing steps typical in fabrication of aesthetic all-ceramic dentalrestorations.

Though not within the scope of the present invention which is directedtowards sintering ceramic dental articles comprising nanopowders tonearly full density, nevertheless, it should be noted that the injectionmolding technology described in Examples 6 and 7 can be used to producedental articles even if access to RP machines is not available. In thelatter case, if is not possible to make enlarged replicas and greenbodies fabricated therefrom as described in Examples 6 and 7, thearticles will have to be presintered without shrinkage and glassinfiltrated as described in U.S. Pat. Nos. 4,772,436 and 5,910,273,which are hereby incorporated by reference. In the case of YTZP zirconiacores, 3G porcelain can be used for both glass infiltration and estheticlayering of the resulting glass-infiltrated cores.

While various descriptions of the present invention are described above,it should be understood that the various features can be used singly orin any combination thereof. Therefore, this invention is not to belimited to only the specifically preferred embodiments depicted herein.

Further, it should be understood that variations and modificationswithin the spirit and scope of the invention may occur to those skilledin the art to which the invention pertains. Accordingly, all expedientmodifications readily attainable by one versed in the art from thedisclosure set forth herein that are within the scope and spirit of thepresent invention are to be included as further embodiments of thepresent invention. The scope of the present invention is accordinglydefined as set forth in the appended claims.

What is claimed is:
 1. A process for manufacturing dental restorationsconsisting essentially of: (a) depositing a layer of a slurry of aceramic material and a binder; (b) curing the layer of the ceramicmaterial and binder; (c) repeating steps (a) and (b) a number of timesby directly depositing a next layer of a slurry of a ceramic materialonto a previous layer to produce a number of layers of ceramic materialwhich are bonded to one another to form a shape of a dental restoration,wherein the layers vary by mechanical properties comprising strength,fracture toughness and wear, to provide a functionally gradientstructure; (d) hardening the shaped material to form the dentalrestoration.
 2. The method of claim 1 wherein hardening comprisessintering or curing the shaped material.
 3. The process of claim 1further comprising burning out the binder prior to hardening step (d).4. The process of claim 3 wherein the binder is removed during thehardening step (d).
 5. The process of claim 1 wherein the hardening stepcomprises sintering the shaped material to full density.
 6. The processof claim 1 wherein the ceramic material comprises alumina, zirconia,mullite, silica, spinel, tricalcium phosphate, apatite, fluoroapatite,hydroxyapatite, or mixtures thereof.
 7. The process of claim 1 whereinthe layers of ceramic material form a selected pattern.
 8. The processof claim 7 wherein the selected pattern is based on a computer assisteddesign.
 9. The process of claim 1 wherein pigments, opacifiers, and/orfluorescing agents are added to the ceramic material prior to depositionthereof.
 10. The process of claim 1 wherein pigments, opacifiers, and/orfluorescing agents are added to the ceramic material after depositionthereof.
 11. The process of claim 1 wherein pigments, opacifiers, and/orfluorescing agents are added to the ceramic material during depositionthereof.
 12. The process of claim 1 wherein the binder comprises aninorganic or an organic material.
 13. The process of claim 1 wherein thebinder comprises a molten thermoplastic material or a wax-containingmaterial.
 14. The process of claim 1 wherein the binder comprisespolycarbosilazane or tetraethylorthosilicate.
 15. The process of claim 1wherein the dental restoration comprises denture teeth, bridges, crowns,space maintainers, tooth replacement appliances, orthodontic parts,orthodontic retainers, dentures, posts, jackets, inlays, onlays,facings, veneers, facets, implants, abutments, splints, partial crowns,teeth, cylinders, pins, and connectors.
 16. A process for producing adental restoration consisting essentially of: providing a mixture ofceramic powder material dispersed in a binder; and dispensing themixture from a dispensing apparatus onto a platform to build afree-standing three dimensional dental restoration layer by layer,wherein each layer is deposited directly onto a previous layer by thedispensing apparatus, and wherein each layer can vary by mechanicalproperties comprising strength, fracture toughness and wear, to providea functionally gradient structure.
 17. The process of claim 16comprising curing a layer before dispensing the next layer.
 18. Theprocess of claim 16 further comprising hardening the free-standing threedimensional dental restoration.
 19. The method of claim 18 whereinhardening comprises curing or sintering the free-standing threedimensional dental restoration.
 20. The process of claim 16 furthercomprising burning out the binder prior to hardening the free-standingthree dimensional dental restoration.
 21. The process of claim 18wherein the binder is removed during hardening the free-standing threedimensional dental restoration.
 22. The process of claim 18 wherein thehardening step comprises sintering the free-standing three dimensionaldental restoration to full density.
 23. The process of claim 16 whereinthe dispensing apparatus comprises a continuous stream print head ordrop-on-demand stream print head.
 24. The process of claim 16 whereinthe mixture is dispensed in the form of a bead, stream, or droplet. 25.The process of claim 24 wherein the bead, stream or droplet comprises aslurry or a liquified filament.
 26. The process of claim 25 wherein theslurry comprises a ceramic powder and a binder.
 27. The process of claim25 wherein the liquified filament comprises ceramic powder and a binder.28. The process of claim 16 wherein the binder comprises an inorganic oran organic material.
 29. The process of claim 16 wherein the bindercomprises a molten thermoplastic material or a wax-containing material.30. The process of claim 16 wherein the binder comprisespolycarbosilazane or tetraethylorthosilicate.
 31. The process of claim16 wherein pigments, opacifiers, and/or fluorescing agents are added tothe ceramic powder material during, after or before dispensing thereof.32. The process of claim 16 wherein the dental restoration comprisesdenture teeth, bridges, crowns, space maintainers, tooth replacementappliances, orthodontic parts, orthodontic retainers, dentures, posts,jackets, inlays, onlays, facings, veneers, facets, implants, abutments,splints, partial crowns, teeth, cylinders, pins, and connectors.